public class test49 {
    public static void main(String[] args) {
        String phoneNumber ="16634449591";
     String str1 =phoneNumber.substring(0,4);//截取字符串0索引到3索引(166)
     String str2 =phoneNumber.substring(7);
        String result =str1+"****"+str2;
        System.out.println(result);
    }

}
